Synthesis And Properties Of Nano-hierarchical Electrocatalyst Based On Ag@C Nanocables

Owing to climate change and the depletion of oil supplies,research and development of clean energy will be crucial in the coming decades.The subject of basic and practical research is progressive clean energy storage and conversion technology,mainly including fuel cells（FC）,electrocatalytic water splitting（EWS）,and metal-air batteries（MABs）.The foundation of the above-mentioned various energy storage and conversion technology is electrochemical oxidation and reduction reactions.Among them,the redox reactions between water,oxygen and hydrogen played a vital role in energy storage and conversion technology.The main reactions include oxygen reduction reaction（ORR）,oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）.To accelerate the practical application of these energy equipment,we need to synthesize highly efficient ORR,OER and HER electrocatalysts,which can lower the reaction energy barrier and eventually improve energy efficiency.At present,the most advanced oxygen and hydrogen electrocatalytic active materials are precious metals and their compounds（Pt/C is used for ORR and HER,Ir O2 is used for OER,etc.）.Due to the limited reserves and the high cost of precious metals,non-platinum-based and non-iridium-metal-based materials have been studied as alternative materials for electrocatalysis.For these electrocatalysts with metal-based active moieties,materials with one-dimensional,two-dimensional,or three-dimensional hollow structures can be used as multifunctional carriers to enhance charge and mass transfer.Especially,combining one-dimensional structure,two-dimensional structure or three-dimensional hollow structure with metal-based active moieties to construct a new type of electrocatalyst with hierarchical structure can effectively improve the catalytic efficiency.In this thesis,one-dimensional core-shell structured Ag@C nanocable are used as a carrier and combined with transition metal-based active moieties to construct a series of hierarchical electrocatalysts,and systematically studied its catalytic performance and reaction mechanism,the main contents are as follows:Firstly,we summarized some of the redox reactions between water,oxygen and hydrogen,and briefly described the electrocatalytic storage and conversion devices composed of the above reactions,researched the electrocatalyst used in the oxidation-reduction reaction between water,oxygen and hydrogen in recent years,emphasized the importance of constructing an electrocatalyst with a hierarchical structure in the redox reaction between water,oxygen and hydrogen,and expounded the background and research content of this thesis.Secondly,using Ag@C nanocables with one-dimensional core-shell structure as the carrier,using 2-methylimidazole（2-Me IM）and cobalt nitrate（Co（NO3）2 · 6H2O）as raw materials,and polyvinylpyrrolidone（PVP）as surface active agent,ZIF-67 dodecahedrons are uniformly grown on Ag@C nanocables to get Ag@C@ZIF.After that,using Ag@C@ZIF as precursor,calcined at the optimum temperature under ammonia（NH3）or nitrogen and hydrogen mixed flow（N2/H2）to obtain NH3-Ag@C@ZIF-700 and N2/H2-Ag@C@ZIF-450 electrocatalyst,respectively.By characterizing the morphology and structure,it can be found that the two electrocatalysts prepared have obvious hierarchical structures.Electrocatalytic oxygen reduction tests for the obtained electrocatalyst were perform.Through the results,it can be found that the ORR activity of NH3-Ag@C@ZIF-700 is higher than that of the precious metal catalyst（Pt/C）and the ORR activity of N2/H2-Ag@C@ZIF-450 is comparable to that of precious metal catalysts（Pt/C）.Thirdly,using Ag@C@ZIF as the precursor,then,the precursor was etched with Mo O42-under the condensed reflux condition to obtain Ag@C@Co Mo-LDH electrocatalyst.The characterizations of morphology and structure for Ag@C@Co Mo-LDH electrocatalyst showed that the Ag@C@Co Mo-LDH electrocatalyst is formed by assembling a three-dimensional hollow structure composed of sheet hydroxides on the Ag@C nanocables,with obvious hierarchical structure.The electrocatalytic activity of Ag@C@Co Mo-LDH electrocatalyst was tested.The results demonstrated that the Ag@C@Co Mo-LDH electrocatalyst exhibited excellent activities for OER,HER and water splitting.Fourthly,using Ag@C@ZIF as the precursor,using ferric nitrate and nickel nitrate as the iron source and nickel source,respectively,the template was converted under hydrothermal conditions to obtain the Ag@C@CoFeNi-LDH electrocatalyst.Through the characterization of the morphology and structure,it can be found that the Ag@C@CoFeNi-LDH electrocatalyst is formed by assembling the flake hydroxide onto the Ag@C nanocables,and has an obvious hierarchical structure.The electrocatalytic activity of Ag@C@CoFeNi-LDH electrocatalyst was tested.The results demonstrated that the Ag@C@CoFeNi-LDH electrocatalyst exhibited excellent activities for OER,HER and water splitting.In summary,we have synthesized a series of electrocatalysts with hierarchical structure that combine core-shell Ag@C nanocables with transition metal-based active moieties,and conducted physical characterization and electrocatalytic performance tests.The results show that the synthesized electrocatalysts with hierarchical structure have excellent ORR or OER,HER and electrocatalytic water splitting activities,which provide a new idea for the rational construction of hierarchical electrocatalysts.